In tobacco industry, semi-finished products in form of filtering or cigarette rods, as well as final products in form of cigarettes, cigarillos or cigars, are transported between machines at manufacturing lines in a form of a multilayer flow, also called a mass flow. The mass flow is conducted by horizontal, inclined and vertical conveyors. Additionally, vertical or inclined gravitational ducts are utilized. At the connection points between different kinds of ducts, buffering reservoirs are usually used, to compensate for different flow efficiencies of connected ducts, in order to change the flow parameters over time. The connected ducts may have different cross-sections and different flow efficiencies.
In the state of the art there are known various connections between ducts, for example such as disclosed in the following patent publications: GB 1276494, U.S. Pat. No. 4,030,595, GB 2 029 787 or DE 1957002, which disclose a connection between two horizontal ducts equipped with conveyors and a gravitational duct, wherein the horizontal ducts are the feeding ducts, while the vertical duct is the receiving duct. From the vertical duct, products are received by a packaging machine or, generally speaking, by a receiving machine. The presented reservoirs have adjustable capacity and are equipped with rigid swinging elements, elastic elements or net-like elements with loosely connected mesh for reading the filling level of the reservoir.
The U.S. Pat. No. 3,921,790 discloses a connection of two horizontal feeding ducts equipped with conveyors with a gravitational duct, wherein the horizontal ducts have different width. In case of decreased efficiency of a machine which receives products from the vertical duct, a temporary excess of products is accumulated in the reservoir, which is detected by a sensor, and the speed of the conveyors is decreased or the conveyors (optionally one of the conveyors) are stopped. In case of a decrease of the amount of the rod-like elements in the reservoir, the flow speed in the ducts is increased or the speed of receiving of the elements is decreased. The presented solutions do not allow for independent speed control of the conveyors in the feeding ducts, because it is difficult to clearly determine to what extent the flows from particular ducts influence the degree of filling of the reservoir.